I do tell the buyers to make sure they understand the rules for their notice.  Then its up to them when they give notice.  I had one once that didn't give notice and didn't understand their lease agreement. They had a lease agreement that was automatically renewed if they didn't give notice 60 days before the end of the lease.  They ended up with a contract to buy and a lease that was renewed for two years. It ended up though alright the person they leased from let them out of their lease.  

Buyers need to understand the rules of their lease and the time line to give notice.   

One situation that took everyone by surprise was that the seller's loan was sold during escrow and that caused a delay because we had to wait for the new servicer to assign a loan number before a payoff statement could be ordered. 

It's one of those weird things that caused escrow to close late and it was not the fault of the buyer or the seller.

If there's a loan on the property, it might be a good idea to have the seller call the bank and ask if their loan is about to be sold.

Best to have plenty of time for moving and potential delays.

It is up to the buyers.

I leave it up to them. It is their call.

Gary Branscombe once the agreement is signed and inspection issues are resolved, I do tell my buyers to give the notice. Not many of my buyers had issues with mortgage commitment.

Good input above.

Another consideration is if they are going to do improvements before they move in (e.g. refinishing floors, painting, hardwood, etc).  Many underestimate the time to do this and get caught in this same situation.

They need to look at all the aspects.  Many need that extra time anyway as things get delayed + improvements get delayed as buyer often doesn't plan well and if closing gets delayed, it may delay contractors who may be booked.

Before commiting, I ask them if they have somewhere to go if it doesn't close on time, or not at all, such as family members.  I let them make the decision.

It ain't over 'til the fat lady, or the mortgage company sings, however, most apartments around here now want a 60 day notice.  I still tell buyers to wait until we are under contract and inspections are done.  You might have a bit of a double payment one month, but that's better than being homeless!

I had this problem when I bought my first house. I gave my notice to move out of my apartment but my loan was delayed, When I asked my apartment manager if I could stay 2 weeks longer I was told my apartment had already been rented! So I had to stay at my sisters house and store my belongings in the moving truck, for nearly a month!

So now I recommend buyers not to give their notice until their loan is funded. There will be some overlap but they can take their time to move in and not stress out..

It's probably a good idea not to give notice until everything is pretty assured.  Even then, problems could arise.

Each situation is unique, but I generally recommend that they wait until they've signed off on contingencies.